Missing Desktop Icons and Taskbar in XP and Vista

I would like one of the experts here to answer this. I assist other people in troubleshooting windows problems. I help people every day and what I have noticed is a severe increase in the number of people complaining about missing desktop icons and taskbar, both in XP and Vista. Do any of the experts here know of a specific virus or trojan infection that targets the desktop taskbar and/or icons (making them disappear or make them unrecoverable)? I would like to know which virus' or trojans are responsible for this by name, if possible, and do Check Point products prevent or remedy these attacks?